(17Nov)A newly discovered volcano rumbling beneath nearly a mile of ice in Antarctica will almost certainly erupt at some point in the future, according to a new study. Such an event could accelerate the flow of ice into the sea and push up the already rising global sea levels.When the volcano will blow is unknown, "but it is quite likely" to happen, Amanda Lough, a graduate student in seismology at Washington University in St. Louis, Mo., told NBC News."At some point, it is going to erupt," she said. "Is it going to erupt in any of our lifetimes? That is not something that we can pinpoint."And when it does erupt, she added, "there would be an increase in melting around the area. … You would add water to the system beneath the ice sheet … and that could cause that ice stream to speed up."In other words, global warming likely isn't the only factor causing sea levels to rise, and the discovery of a subglacial volcano adds another layer of complexity for scientists trying to model how polar ice sheets move as the world gets warmer. But what overall impact this might have on global sea levels is unknown — and up for debate.,,,

A map of the earthquakes in the Canterbury earthquake sequence around Christchurch, New Zealand. Stars note the largest events, with intervening aftershocks in the same color (red is the Sep. 3, 2010, magnitude-7.1 earthquake; black is the Feb. 22, 2011,

New Zealand Earthquakes Weakened Earth's Crust

A series of deadly earthquakes that shook New Zealand in 2010 and 2011 may have weakened a portion of Earth's crust, researchers say. DCI New Zealand lies along the dangerous Ring of Fire — a narrow zone around the Pacific Ocean where about 90 percent of all the world's earthquakes, and 80 percent of the largest ones, strike. A devastating magnitude- 6.3 quake struck New Zealand's South Island in 2011. Centered very close to Christchurch, the country's second-largest city, it killed 185 people and damaged or destroyed 100,000 buildings. The earthquake was the costliest disaster to ever strike New Zealand, consuming about one-sixth of the country's gross domestic product.

This lethal earthquake was the aftershock of a magnitude-7.1 temblor that struck 172 days earlier (in 2010) in the area, causing millions of dollars in damage to bridges and buildings, and seriously injuring two people. Although the 2010 temblor was stronger than its aftershock, it caused less damage because it occurred farther away from any city. The 2011 earthquake was, in turn, followed by a number of large aftershocks of its own.

Scientists found that most of the earthquakes that struck New Zealand during these two years released ABNORMALLY HIGH LEVELS OF ENERGY, consistent with those seen from ruptures of very strong faults in the Earth's crust. The scientists analyzed seismic waves detected before and after the quakes. Based on this data, including seismic waves from more than 11,500 aftershocks of the 2010 quake, they mapped the 3D structure of the rock under the Canterbury Plains, similar to the way ultrasound data can provide an image of a fetus in a womb. (photos)Canterbury earthquakes were HIGHLY UNUSUAL - The Canterbury earthquakes were even more unusual than first thought and unlikely to occur anywhere else in the world, new research reveals.

Research showed the UNUSUAL ROCK STRUCTURE of the region meant the Canterbury earthquakes produced some of the strongest vertical ground accelerations EVER SEEN in an earthquake. The makeup of this unique dense and thick slab of rock could have implications for other regions around the lower South Island. ''There will be few other places in the world where a similar earthquake sequence might occur."

The research showed that the strong quakes in Canterbury also could cause widespread cracking and weakening of the earth's crust - challenging the common assumption that the strength of the crust was constant. Normally rocks become hot and ''plastic'' at depths of about 10km. However, the researchers found that strong, brittle rocks continued to a depth of about 30km under Canterbury. ''Strong rocks store and release strain differently to weak rocks."

This UNUSUALLY thick and dense slab of rock helps to explain the long and energetic aftershock sequence in Canterbury. Seismic energy would have dissipated more quickly in softer rock.The researchers were now focussed on determining how widespread this strong rock unit is in the lower half of the South Island. "This is important for defining the earthquake hazard for people living between mid-Canterbury and Southland."

Researchers found that rock properties had changed significantly over a wide area around the Greendale Fault, which ruptured on 4 September 2010 producing a magnitude 7.1 quake. "This finding was entirely unexpected, but it explains why the main shock released so much energy." Most of the quakes in the two-year-long Canterbury sequence released ABNORMALLY HIGH LEVELS OF ENERGY - this was consistent with the ruptures occurring on very strong faults that store energy slowly and gradually and are hard to break. The Canterbury quakes had their genesis 100 million years ago when very strong rocks became emplaced under Canterbury.

The delay between the September 2010 and Feburary 2011 quakes also may have been caused by a ''strength recovery'' required for the crust following the cracking following the September quake.

---------....

Widespread weakening

Approximately 6 miles (10 kilometers) below the Canterbury Plains lies a large, extremely strong block of volcanic rock called the Hikurangi Plateau, which was pulled underground about 100 million years ago, when the portion of the Earth's surface it rested on dove under the edge of the ancient supercontinent Gondwana. It remains attached to Earth's crust, welded to chunks of a dark, gray sandstone known as greywacke.

The scientists analyzed seismic waves detected before and after the quakes by GeoNet, a network of seismographs across New Zealand. Based on this data, including seismic waves from more than 11,500 aftershocks of the 2010 quake, they mapped the 3D structure of the rock under the Canterbury Plains, similar to the way ultrasound data can provide an image of a fetus in a womb.

Beneath the surface broken by the quakes, the researchers identified a broad region that appeared to be dramatically weaker after the quakes. This suggests there was widespread cracking of greywacke 3 miles (5 km) around the fault. In contrast, earthquakes of similar magnitude in the crust elsewhere typically only "produce zones of cracked rock around the fault which are a few hundred meters wide," said study lead author Martin Reyners, a seismologist at research institute GNS Science in Lower Hutt, New Zealand.

Until now, scientists had assumed that the strength of Earth's crust remains constant during aftershocks. But these new findings, detailed online Nov. 24 in the journal Nature Geoscience, suggest energetic quakes can lead to widespread weakening of the crust.

"Such widespread weakening is not common, and has not been reported previously," Reyners told LiveScience's OurAmazingPlanet

Why there?

To explain why weakening was seen in that particular region and not elsewhere after strong quakes, Reyners noted the increasing pressure and temperature seen with increasing depth in the crust that usually means that at depths of more than about 6.8 miles (10.9 km), rocks are no longer brittle. As a result, the rocks often flow, not crack, when force is applied to them.

"This is known as the brittle-plastic transition," Reyners said.

However, "because of the very strong rock unit underlying Canterbury, the brittle-plastic transition is very deep — it lies at about 35 kilometers [22 miles] depth," Reyners said. As such, widespread cracking and weakening of the rock occurred.

The researchers will now focus on figuring out how widespread this strong block of rock is at shallow depths throughout the eastern portion of the South Island of New Zealand. "This is important for defining the seismic hazard for communities in this region," Reyners said.

April 4, 2012 – NEW ZEALAND – An international team of scientists have found what they believe are the world’s biggest ” pockmarks” — craters formed by seafloor eruptions of gas or fluids — in waters off New Zealand. The New Zealand, German and U.S. scientists found the pockmarks at a depth of about 1,000 meters on the seafloor of the Chatham Rise, about 500 km east of Christchurch. The three giant pockmarks, the largest measuring 11 km by 6 km in diameter and 100 meters deep, were possibly twice the size of the largest pockmarks recorded in scientific literature, said a statement from New Zealand’s Institute of Geological and Nuclear Sciences (GNS Science). The craters were part of a much larger field of thousands of smaller pockmarks that extended eastward along the Chatham Rise for several hundred kilometers. “Some of the pockmarks on the Chatham Rise are huge compared to similar structures observed elsewhere in the world,” GNS Science marine geophysicist Bryan Davy said in the statement. “They are big enough to enclose the Wellington city urban area, or (New York’s) lower Manhattan.” Gas release from the larger pockmarks could have been sudden and possibly even violent, with a massive volume expelled into the ocean and atmosphere within hours or days. Scientists could not rule out volcanic activity having caused the release of gas, but another possibility was the release of sub- seafloor hydrocarbon gas, which would have coincided with drops in the sea level of about 100 meters during ice ages and subsequent warming of sea temperatures. University of Auckland gas hydrate scientist Ingo Pecher said there was no sign of active gas systems in the larger pockmarks, but the smaller ones in shallower water appeared to have been sporadically active.

(11Dec)A big, hot blob hiding beneath the bottom of the world could be evidence of a long-sought mantle plume under West Antarctica, researchers said Monday (Dec. 9) here at the annual meeting of the American Geophysical Union.

The possible hotspot — a plume of superheated rock rising from Earth's mantle — sits under Marie Byrd Land, a broad dome at West Antarctica's edge where many active volcanoes above and below the ice spit lava and ash. The hot zone was discovered with seismic imaging techniques that rely on earthquake waves to build pictures of Earth's inner layers, similar to how a CT scan works. Beneath Marie Byrd Land, earthquake waves slow down, suggesting the mantle here is warmer than surrounding rocks. The strongest low-velocity zone sits below Marie Byrd Land's Executive Committee Range, directly under the Mount Sidley volcano, said Andrew Lloyd, a graduate student at Washington University in St. Louis.

"The slow velocities suggest that it's a mantle hotspot," Lloyd said. The hot zone also matches up with Marie Byrd Land's high topography and active volcanoes, Lloyd said.

Mantle Plume?

Many researchers have long suspected that Marie Byrd Land sits atop a hotspot, because the region swells above the surrounding topography like the top of a warm soufflé (and it has lots of volcanoes). But with few seismometers sitting on the ice, scientists were left speculating about what lies beneath Antarctica's ice

The evidence for the new hot zone, called a thermal anomaly, comes from a massive, temporary earthquake-monitoring network called Polenet that was installed between 2010 and 2012, giving scientists an unprecedented look at Antarctica's crust and mantle. (A gravity survey conducted at the same time also suggests there is a big warm spot beneath this part of West Antarctica.)

But confirming that Marie Byrd Land is truly above a hotspot may require a return trip to Antarctica for another seismic experiment, said Doug Wiens, principal investigator on Polenet.

"What's absolutely sure is there's a big thermal anomaly, a big blob," said Wiens, a seismologist at Washington University. "What's less sure is whether that anomaly goes deeper."

The thermal anomaly extends 125 miles (200 kilometers) below Marie Byrd Land, Lloyd said. Below about 255 miles (410 km), where a mantle plume's trailing tail would also leave a hotter-than-average mark in mantle rocks, there's little evidence for a rising hotspot, said Erica Emry, a postdoctoral researcher at Pennsylvania State University.

"But confirming that Marie Byrd Land is truly above a hotspot may require a return trip to Antarctica for another seismic experiment, said Doug Wiens, principal investigator on Polenet."Pero aqui,especulamos.

December 13, 2013 – ANTARCTICA - It’s official: East Antarctica is pushing West Antarctica around. Now that West Antarctica is losing weight–that is, billions of tons of ice per year–its softer mantle rock is being nudged westward by the harder mantle beneath East Antarctica. The discovery comes from researchers led by The Ohio State University, who have recorded GPS measurements that show West Antarctic bedrock is being pushed sideways at rates up to about twelve millimeters–about half an inch–per year. This movement is important for understanding current ice loss on the continent, and predicting future ice loss. They reported the results on Thursday, Dec. 12 at the American Geophysical Union meeting in San Francisco. Half an inch doesn’t sound like a lot, but it’s actually quite dramatic compared to other areas of the planet, explained Terry Wilson, professor of earth sciences at Ohio State. Wilson leads POLENET, an international collaboration that has planted GPS and seismic sensors all over the West Antarctic Ice Sheet. She and her team weren’t surprised to detect the horizontal motion.,,,http://www.spacedaily.com/reports/East_Antarctica_is_sliding_sideways_999.html